Wrote letter of 1676-11-27 (AB 29) to Henry Oldenburg
Text of the letter in the original Dutch and in English translation from Alle de Brieven. The Collected Letters at the DBNL - De Digitale Bibliotheek voor de Nederlandse Letteren
Leeuwenhoek wrote this letter to Henry Oldenburg, but it is now lost. There is no manuscript. It is mentioned in Letter 21 of 1677-10-05 (AB 33), written to Oldenburg after this death. It may also be what Leeuwenhoek referred to in his letter of 1677-02-15 to Christiaan Huygens:
If you should receive any comment on my last observations on the louse (which I learn from your father you intend to translate into French and to send to France) I beg you kindly to communicate it to me.
If that's true, Leeuwenhoek sent a copy of this letter to Constantijn Huygens, who gave it (or a copy) to his son Christiaan, so it is doubly lost!